The Wilms' tumor 1 protein is a developmental transcription factor that can either activate or repress genes involved in growth, apoptosis and differentiation. How these disparate activities of WT1 are regulated is not clear, but have important implications in determining its role in multiple cancers. Our long-term goal is to understand the mechanisms by which WT1 regulates transcription in development and disease. BASP1 is a critical regulator of WT1 that switches its function from a transcriptional activator to a repressor, and acts by binding to WT1 at the control regions of target genes. We have made the novel finding that the N-terminal myristoylation of BASP1 and the capacity of BASP1 to interact with phosphatidyinositol 4,5-bisphosphate (PIP2) is critical for its transcriptional cosuppressor function. Moreover, our recent data demonstrate that BASP1 is part of a large multiprotein complex that contains the transcriptional repressor prohibitin and histone deacetylase activity. The goal of the current proposal is to provide critical new insights into the mechanisms involved in the regulation of transcription by WT1-BASP1 and the novel role of PIP2. The specific aims are to; 1. Elucidate the mechanisms by which BASP1-PIP2 interactions control the transcription function of WT1. The role of PIP2 in transcriptional regulation by WT1-BASP1 through chromatin remodeling and RNA polymerase II activity will be investigated using ChIP, transcription analysis, and colocalization approaches. These studies will provide new insights into a novel mechanism of transcriptional repression by gene-specific regulators. 2. Isolate the components of the BASP1 complex and study their function in WT1 regulation. We have recently identified the transcriptional repressor prohibitin and histone deacetylase I as components of the BASP1 complex, which will be analyzed further to determine their mechanism of action. The other components of the complex will be identified and their role in BASP1-mediated transcriptional repression elucidated. 3. Determine the role of the BASP1 complex and PIP2 in the control of differentiation by WT1. A cell line model of podocyte differentiation that is dependent on the activities of WT1 and BASP1 will be employed to identify the critical components of the BASP1 complex, and uncover the role of PIP2 in WT1-dependent gene expression that drives the differentiation process.